1. Field of the Invention
The present invention relates to a miniature surface-mount electronic component in which a coil wound on a ferrite core is resin-molded. A miniature surface-mount electronic component according to the present invention includes an antenna applicable to a vehicle-mounted transponder or the like, an inductor for a communication device, a choke coil or the like.
2. Related Art
Various types of miniature surface-mount electronic components have been conventionally proposed, and have been in practical use. As one of them, a miniature surface-mount electronic component applicable as a vehicle-mounted antenna or a transponder has been proposed recently. In miniature surface-mount electronic components applied to such a use, cores made of ferrite favorable in high-frequency characteristic are generally used. The configuration in which a coil wound on the core by the required number of windings, and an outer periphery of the core including the winding wire with the winding wire terminals of the coil connected to metal terminals provided at both ends in a longitudinal direction of the core are molded of an insulating resin is adopted.
In order to satisfy the required characteristics such as an inductance value, a Q value and self-resonance frequency characteristics required of this kind of coil, a core slim and longer in a winding axis direction of the coil is generally used as a core.
However, the core is a brittle sintered body, and is originally weak against impact and vibrations as earthenware. In addition, for the above described reason, the core tends to be weak against impact and vibrations, and cannot help being formed into a slim and long shape. Therefore, in the case of the vehicle-mounted coil which is always exposed to impact and vibrations, it is important how to realize the structure excellent in impact resistance and vibration resistance.
From such a point of view, for example, Japanese Patent Laid-Open No. 7-130556 discloses a coil which is entirely covered with resin molding.
Japanese Patent Laid-Open No. 2003-31803 discloses the coil improved in impact resistance and vibration resistance by covering the entire body with an insulating resin, and putting some contrivance into the shape of a core, the terminal structure and the like.
However, in these coils, core breakage due to the terminal holding structure of the core becomes a problem. There exist the problems of core breakage occurring because positional displacement or the like of the coil occurs in the molding process of coating the entire body with an insulating resin and the terminals are fixed, and wire breakage occurring because fixation of the terminals and the core becomes loose and the winding terminals are pulled.
The present invention is made in view of the above described problems, and has an object to provide a miniature surface-mount electronic component which can ensure sufficient impact resistance and vibration resistance especially in an application to a severe use environment such as a vehicle-mounted coil, by putting some contrivance into a method for fixing a coil in a molding process and a method for holding a core and terminals.